The present invention relates to thin film recording heads, and more particularly to a thin film head with minimized secondary pulses.
Thin film magnetic recording heads are well-known for recording of digital data on a recording medium. A typical two-pole head 10 in a disk drive assembly 11A of computer 11, shown in FIG. 1, includes poles P1 and P2 extending along a longitudinal axis Y. Respective ends of these poles are coupled together to form yoke 12 at a distal end of head 10. At the proximal end of the head the poles terminate in respective pole tips 14, 16. The poles are formed separated by a gap g having a gap thickness g.sub.t (along the X-axis). The pole tips terminate in a polished air bearing surface (ABS) at the end of the gap. The head is typically formed with excess material at the pole tips, which are then carefully lapped back to establish the ABS at a desired throat height h.
The gap forms a pole throat T, having a height h extending along the head longitudinal axis between the parallel pole tip inside walls 15, 15'. Height h is measured from the point where walls 15, 15' no longer diverge called the zero throat height point (ZTH) to the ABS. The gap thickness g.sub.t is carefully controlled over the height h of the pole throat T for uniformity of magnetic response and optimized magnetic performance. The pole tips are generally rectangular from the ABS to the ZTH, and conventionally measure several microns in height.
The pole tips cooperate with medium 20 as it streams past the head in direction 22 tangent to or along the X-axis. The pole tips 14, 16 interact with the recording medium for writing data onto or reading data from the medium. The head has a width measured along the Z-axis which defines the head "footprint" (i.e., track width) on the medium.
For a portion or all of throat height h, the pole tips extend perpendicularly from the ABS toward yoke 12, during which both pole tips are essentially rectangular. Thereafter, while the P1 pole essentially continues extending generally perpendicularly back to the yoke, the P2 pole tip 16 begins to turn into ramp 21, at an acute takeoff angle A, and then a back portion 23 of the P2 pole ultimately couples the P2 pole into the yoke.
The magnetic head generates write fields which represent data sought to be stored in magnetic layer 20' of the medium as the medium is moving in direction 22 at a constant speed. The magnetic material layer includes magnetic dipoles which can be oriented in a given direction in tracks in response to the head's magnetic write field. A change or "transition" in dipole orientation represents a stored bit on the recording medium. The goal in making a head for high density recording is to obtain a very narrow gap thickness g.sub.t over the pole throat height h, because it is the narrowness of the gap which in large measure determines the size of the recorded bit (the number of dipoles transition to transition), and hence recording density.
Generally speaking, a read flux circuit, beginning with flux from the medium, runs through one of the pole tips through the yoke and returns to the medium via the other pole tip. In an inductive head, an inductive pickup coil 18 is provided to interact with the flux passing through yoke 12 in order to generate a readback voltage based on the flux rate of change in the read flux circuit. Ramp 21 opens up the head between the poles to facilitate formation of coil 18 around the yoke. Coil 18 is coupled to a downstream data qualification circuit 11B of computer 11 within which the data signal is extracted from the readback signal for conversion into useful information.
The two-pole head reads a transition in three steps, thus generating the readback signal 26 shown in FIG. 2. First, flux from an oncoming transition on the medium links into the leading edge 34 of pole tip 14 from which a leading secondary pulse 30 is generated. Next, as the transition continues to move past the head from the first pole tip, across the gap, to the leading edge 36 of the second pole tip 16, a main pulse 28 is generated. Now as the transition moves away from the head, its flux decouples from the trailing edge 38 of the second pole tip 16 and generates a trailing secondary pulse 32. Secondary pulses 30, 32 are typically of the same polarity, but of a polarity opposite to that of the main pulse 28, and while the main pulse is generally a high frequency signal, the secondary pulses have a lower frequency component. It is on these bases that the main and secondary pulses are distinguished by qualification circuit 11B.
Readback waveform 26 is read within a processing time frame F (measured in microseconds) by the data qualification circuit 11B, and a main pulse 28 is thereafter extracted from the readback waveform representative of a data bit. A plurality of data bits are retrieved by qualifying sequentially generated readback waveforms 26 in a sequence of spaced apart time frames.
The process of high density recording reduces the amplitude of the main pulse 26 generated from reading one of many closely spaced bits to approximately 50 percent of an isolated pulse. Furthermore, where bits are densely packed on a storage medium the trailing or leading secondary pulses from the neighboring bits overlap the main pulse, which further reduces the amplitude of the main pulse to about 30-36 percent of an isolated pulse (about 4-10 percent reduction caused by the leading pulse and about 10 percent reduction caused by the trailing pulse), and makes isolation of the main pulse a more difficult task for the qualification circuit 11B.
It is therefore an object of the present invention to provide a thin film recording head which minimizes secondary pulses in the readback waveform.
It is another object of the present invention to provide a thin film head which eases the task of the qualification circuitry by reducing the effect of secondary pulses in the readback signal.